This invention relates to a shake (or jiggle) correction device mounted on an optical device such as a camera and more particularly to a shake correction device for correcting the deterioration of an image due to shake by use of a wedge prism whose index of refraction is electrically changed.
Conventionally, when photographing is made by use of a camera held in hand, a problem of deterioration of an image due to shake caused at the time of photo-graphing occurs and various techniques are developed to solve the problem. The shake correction technique is widely applied to an optical device such as a binocular in addition to a camera.
Generally, in a film camera, a technique using a shake preventing lens which is disposed in a photo-graphing lens system and moves to prevent the vibration of an image and a driving mechanism for driving the lens is known.
However, use of the driving mechanism for the shake preventing lens makes the photographing lens system larger and since the lens is mechanically driven by the driving mechanism, the movement of the lens cannot follow the shake and a time delay occurs in the shake preventing operation in some cases.
Further, in a camera having an image sensing device such as a CCD, there is provided a shake correction device in which a light receiving area (total pixel number) of the CCD image sensing device is set larger than a light receiving area (effective pixel number) for actually converting received light into an image and which is used for detecting a movement vector of image data photographed by pixels in a preset position and correcting the image itself by an electrical process. However, in the shake correction device utilizing the image sensing device, there occurs a problem that the image quality is lowered and the image processing operation is complicated.
In Jpn. Pat. Appln. KOKAI Publication No. 06-148730 filed by the applicant of this invention, there is proposed an optical shake correction device as the shake correction device using an electrical polarizing member, that is, a liquid crystal prism (wedge prism) which can change the inclination of a light beam passing therethrough according to a voltage applied thereto without using a mechanical driving mechanism.
The shake correction technique is a technique for using a wedge prism formed by sealing a liquid crystal which is an optical anisotropic medium into a space defined by two glass plates combined to form a wedge shape and applying a voltage corresponding to a detection signal detected by an acceleration sensor to the wedge prism so as to,change the index of refraction and deflect the light beam in a direction opposite to the shake direction, thus moving the image to correct the shake.
When the wedge prism in the technology disclosed in Jpn. Pat. Appln. KOKAI Publication No. 06-148730 is used, there occurs a problem that the wedge prism must be driven by use of the open loop control process.
That is, in a conventional vibration preventing device of a type for driving the lens or displacing part of the optical system, a correction amount can be detected by use of some sensor. By feeding back the correction amount, an adequate correction amount can be controlled.
However, in the wedge prism, since the external shape does not change even if a voltage is applied thereto, the correction amount cannot be fed back and it is impossible to monitor whether or not the wedge prism inclines the light beam as designed.
Further, a variation occurs in the physical characteristic of the wedge prism caused at the time of manufacturing and the characteristic cannot be unconditionally set.
Therefore, when the wedge prism is used in the shake correction device of the camera, it is necessary to previously get information on the relation between the driving voltage and the inclination of the light beam passing through the wedge prism for each wedge prism.